The present invention relates to wound drainage systems.
During surgery and afterwards, during recovery, it is often necessary to remove fluid and wound secretions from the site of the wound.
Although previously vacuum pumps were used, it is now conventional to use vacuum suction flasks.
The suction flask is evacuated to a high level of vacuum, normally around 600 to 700 mm Hg. A flexible tube is connected to the flask and the other end of the tube is connected to a perforated wound drainage tube. The wound drainage tube, in turn, is introduced into a hermetically sealed wound cavity. When the line from the flask is opened, the negative pressure prevailing in the flask acts in the wound cavity thus drawing off wound secretions down the line into the flask.
Once the flask is full or the vacuum is no longer sufficient to draw off fluid, the system may be safely disposed of.
Flasks as described above are well-known and such flasks are disclosed in, e.g. EP-A-288679 and Swiss Patents 596,840 and 584,037. However, as stated above, these flasks are charged with a high vacuum, e.g. around 96 kPa (720 mm Hg) and substantially all of that vacuum acts on the patient.
In certain medical applications, however, such high vacuums cannot be applied to the patient. This is particularly the case in e.g. cranial or abdominal surgery where a much lower vacuum, in the region of 13.3 to 20 kPa (100 to 150 mm Hg) is needed at the patient end of the wound drainage line.
Systems have, therefore, been developed to reduce the vacuum from a high vacuum suction flask. One such system is disclosed in EP 0 616 815.
In this system, the vacuum in the flask is adjusted to the desired level by first attaching a pressure measuring device to the neck of the flask. A valve is arranged between the flask and an adjustment device. The measuring device and adjustment device control the opening of the valve until the desired pressure is reached. The adjustment device is then removed and the wound drainage line is attached to the now low vacuum suction flask.
This system, however, is cumbersome and inefficient. It is only used to adjust the vacuum before use. Normally, however, flasks are supplied in a ready-charged, high vacuum state, ready to be attached to the wound drainage line. It would therefore be desirable to provide a vacuum regulating system which can be attached to a standard high vacuum flask and which regulates the vacuum at the patient end during use if a low vacuum system is required.
WO 99/05319 discloses a wound drainage bottle which, in one embodiment, has a vacuum reducer to regulate vacuum levels in order to maintain a constant vacuum in the bottle throughout the entire filling process.
For reasons of economy and convenience, a maximum vacuum is desirable in the suction flask in order to enable the greatest amount of wound secretion to be sucked into the flask before another flask is needed. However, as discussed above, in systems where the vacuum in the flask acts directly on the wound, the suction level in the wound region is too high for some applications.
Also, it is now common practice to use disposable wound drainage systems and, therefore, the cost of manufacture should be kept as low as possible whilst maximizing the capacity of each flask.
One known way of stepping down the vacuum from the flask to the patient is to use clips on the flexible wound drainage tube to reduce its cross-section. The system disclosed in DE-B-2356480 uses a flexible tube clip which causes the cross-section of the wound drainage tube to be closed to a certain extent for regulation of the internal pressure of the vacuum container. With this system, however, it is not possible to ensure that outside the sharply constricted cross-section of the flexible tube, a constant negative pressure largely independent of the negative pressure prevailing in the container can be maintained.
The system disclosed in EP-B-0482029 aims to provide a flexible tube clip with a simple way of reducing the cross-section of a flexible tube in order to form a throttle restriction. When used in a tube connection between a vacuum suction flask and a wound drainage tube, this clip can act independently as a throttle valve.
This system and other known systems use a bellows-type arrangement, integrally formed in a cap attached to the suction flask.
In the bellows system, two pivotal arms are fastened to a bellows arranged on the outside of the cap such that when the bellows are contracted, the arms close together compressing the cross-section of the tube lying between them. When the tube clip is open, the same negative pressure prevails in the tube as in the flask. The same negative pressure is also formed in the bellows. This causes the bellows to contract thus closing the arms of the clip which compress the tube. The resulting reduced negative pressure consequently acts in the wound drainage tube. With the tube closed, the flow from the wound has the effect of raising the pressure in the suction tube and bellows. This allows the bellows and thus the tube to open slightly passing fluid into the flask and again reducing the vacuum. Thus, in operation, the bellows continually regulate and maintain a fairly constant tube opening.
Although this system performs well, effectively and accurately reducing the vacuum to the desired level it does have several disadvantages. In particular, the regulation system is formed as an integral unit with the vacuum flask. It is thus necessary to purchase the whole system for a low vacuum requirement rather than converting an already charged high vacuum bottle for low vacuum use if desired.